The present invention relates to a process of the production of methanol and/or dimethyl ether and/or other oxygenates thereof, an H2-rich and a CO2-rich stream. Further, the invention relates to an integrated plant for the production by said process of methanol and/or dimethyl ether and/or other oxygenates thereof, a H2-rich and a CO2-rich stream. The invention also relates to the use of H2 formed by the shift reaction in a shift reactor for the reduction of CO and CO2 in a methanol synthesis reactor. A flexible use of hydrogen in such a plant and for different uses is disclosed.
Due to the continually stricter requirements of improved environment and reduced emissions, it is supposed that the products produced by the technology disclosed will achieve increased use and importance. For example methanol in addition to several uses in the chemical industry, may be fed to combustion cell driven vehicles. This will reduce the emission of particles, NOx, SOx and VOC down close to zero values and thereby be particularly important for the improvement of the environment in urban areas. Compared to the conventional motor technology, also the emission of climate gases will be reduced, e.g. by 50%. Several large automobile manufacturers are investing highly to develop and commercialise this technology. DME will correspondingly be a particularly environmentally friendly fuel for the diesel combustion vehicles of today. Fleet tests show that this is absolutely practicable. Hydrogen is frequently referred to as the energy carrier of tomorrow. It is certain that there will exist a significantly increasing hydrogen demand in the refinery industry to remove sulphur and reduce the contents of aromatics and olefins in the fuels produced. A possible new use is as fuel for gas turbines of heat generating stations to thus considerably reduce the emission of CO2 in the production of electrical power.
It is generally accepted that the greenhouse effect and the climate on the earth has a close connection to the human produced CO2 emissions, and the reduction thereof is therefore desirable. In the production of methanol or dimethyl ether or any other hydrocarbon containing oxygenates a synthesis gas can be used comprising a mixture of hydrogen, carbon monoxide and carbon dioxide. In spit of CO2 thus being included as a part of the synthesis step, a total excess of CO2 will be formed being emitted to the atmosphere, e.g. by the burning of natural gas in a steam reformer. The U.S. Pat. No. 4,946,477 describes an IGCC process having a combined methanol synthesis/water gas shift for methanol and electrical power production. An improvement is described by the preparation of methanol from a synthesis gas comprising carbon monoxide and hydrogen by using a three phase or liquid phase reaction technique. The improvement of the process resides in addition of relatively small amounts of water to the liquid phase reactor thus allowing use of a CO-rich synthesis gas for the production of methanol by performing methanol synthesis and water-gas shift reactions in the same reactor.
The tables of said patent indicates that CO2 from significant amounts of CO2 are emitted with the turbine exhaust gas.
U.S. Pat. No. 5,799,482 relates to a process of enhanced heat integration of an oxidant supplemented autoterm reformer and co-generation power station. However, the patent does not relate to the production of methanol.
The U.S. Pat. No. 5,624,964 relates to the integration of a steam reforming unit and a co-generation power station. Neither does this patent relate to a methanol synthesis.
U.S. Pat. No. 5,496,859 relates to a gasification process combined with steam methane reforming to prepare syngas useful for methanol production. An integration with power stations or other hydrogen operated stations does not appear to be disclosed.
A particularly compact and efficient mode of synthesis gas production is by the autothermic reformation (ATR) of natural gas. In an autothermic reformer natural gas is fed with oxygen, air or enriched air, into a combustion chamber. The energy required to operate the endothermic steam reformation reactions is provided by the exothermic reactions between hydrocarbons and/or hydrogen and oxygen. The temperature of the combustion chamber itself may reach above 2000xc2x0 C. Following the combustion chamber, the reaction is brought to equilibrium above a catalyst bed before the synthesis gas escapes the reactor at about 1000xc2x0 C. The size of such a unit will typically be 10 to 15 meter high, having a diameter of 5 to 6 meter. The steam/carbon ratio may be 0.6 to 1.4 or higher. Such an ATR may be operated at e.g. 40 bar or higher. For particular purposes a high pressure may be desirable.
However, the stoichiometry of methanol production provides for the stoichiometric ratio
SN=(H2xe2x80x94CO2)/(CO+CO) being like 2,
whereas ATR will provide for a ratio SN of below 2. This requires that also at ATR CO2 has to be emitted at some site.
Further, there will be different requirements of energy to operate a methanol plant. This relates to the option of separation of air, as well as preheating natural gas and methane, and what shall be shown, to separate and compress CO2. A possibility of providing this energy is by the combustion of hydrocarbons, a.o. by the generation of electrical power in gas turbines, which again results in the formation of CO2.
A feasible way to obtain reduced emissions by the production of methanol (or DME) would be to convert the fuel, e.g. natural gas, into a mixture of hydrogen and carbon oxides by ATR technology, use parts of this gas stream to produce methanol, whereas the other part is shifted to hydrogen and carbon dioxide, separating these two components, using the hydrogen as fuel in a gas turbine and to adjust the stoichiometric relation in methanol production, and to deposit carbon dioxide subsequent to compression to the desired pressure. This deposition may take place on the seabed or in geological reservoirs. These reservoirs may include hydrocarbons. Depending on the requirement of methanol and/or energy, the total energy balance, local conditions, the value of the single product streams etc., the ratio between said synthesis gas streams may be varied liberately. As an extreme it will not be necessary to produce electrical power in a gas turbine.
Such a technology as disclosed above is costly and will result in a smaller energy yield than a conventional, but modern production plant. It is thus a challenge to design the process as economically optimal as possible and reduce the energy consumption to a minimum, a.o. through heat integration and an optimal steam balance. To achieve this it may be suitable to operate the single process steps in a different and simpler way than usual if hydrogen, carbon monoxide or synthesis gas are to be used in industry, e.g. in petrochemical industry or by refining raw oil. This profit in simplified plants may be achieved by allowing that a limited part of the carbon feed stock resides in the form of methane or carbon monoxide when the hydrogen-rich gas mixture is fed as a fuel to the gas power station. The reforming of natural gas, shift of carbon monoxide to carbon dioxide as well as the separation of carbon dioxide will thus be feasible at conditions beneath those being generally accepted in industry and recommended in textbooks.
A particularly beneficial result of the reduced requirement of methane and carbon monoxide in the product gas will be the possibility of operating one or more process steps at a higher pressure. Thereby a reduction in costs and in the compression energy of CO2 prior to deposition is obtained. It may thus also be possible to separate and compress CO2 in a liquid form, which may result in further savings. Other savings result in the possible use of lower temperatures in reforming than would else be required at a given pressure. Further if both low temperature shift and methanisation of residual carbon monoxide may be unnecessary, different from what is standard technology today in the production of hydrogen for the synthesis of ammonia. If separating CO2 in an amine washing process is selected, this may be simplified, e.g. by only using a limited depressuration instead of steam stripping.
The following chemical reactions are central in the production of synthesis gas, methanol and hydrogen in the reformation of natural gas:
The reaction heat of the strongly endotherm steam reformation may be provided either by external burning or by the combination of the exothermic partial oxidation in an autotherm reformer. A purely partial oxidation of the combined reforming may also be used.